Lens antennas could be utilized as receiving and transmitting antennas in many applications, but have many practical disadvantages including high weight, complex surface form and thickness that have limited their implementation. The problem of complex surface form can be addressed by forming the antenna lens from a flat piece of inhomogeneous dielectric material. While such lenses have certain unique features that cannot be achieved with lenses formed of a uniform dielectric, they do not solve the problems of weight and thickness associated with lens antennas.
A rectangular or circular slab of dielectric material has an index of refraction n(R) that is a function of radius as given by the following equation: EQU n(R)=n(0)sech(.pi.R/2F)
where n(0)&gt;1 and F is a thickness of the lens which exhibits a focusing effect. The ratio F/D, where D is a diameter of the lens, is given by the equation: EQU F/D=(.pi./4)/sinh.sup.-1 (1/n(0))
For n(0)=2, the F/D ratio is equal to 0.544, which means that the lens thickness is more than half of the antenna diameter. Such an antenna structure would be to thick and heavy for most practical applications. While zoning could be used in an attempt to address problem of thickness and the associated problem of weight, the operating band of the antenna becomes narrower as the number of required zones increases, thereby rendering the antenna ineffective for many applications.
In view of the above, it is an object of the invention to provide a wideband lens antenna incorporating an antenna lens of reduced thickness. It is a further object of the invention to provide an antenna lens of simplified surface structure and reduced weight as compared with conventional antenna lenses.